A New Approach to the Archean Sulfur Cycle from Marine Carbonates

California Institute Of Technology, Pasadena CA

Investigators

Abstract

A New approach to the Archean sulfur cycle from marine carbonates By Jess Adkins, Woodward Fischer ABSTRACT The rise of atmospheric oxygen from an originally reduced planet surface is a central problem in Earth history. It is widely believed that the oxygenation of the Earth's oceans and atmosphere occurred in abrupt steps. The Great Oxygenation Event at the Archean-Proterozoic boundary is one of the better studied of these deep-time jumps, chiefly through the mass independent fractionation (MIF) of the stable sulfur isotopes. However, most of this evidence comes from the reduced forms of sulfur, chiefly pyrite being enriched in the MIF signal. The current understanding assumes that the complementary light MIF signal resides in oceanic sulfate at this time, a trace phase in carbonates that has been analytically inaccessible until now. PIs will use a new MC-ICP-MS method that lowers the current detection limit for sulfate in Archean carbonates by over three orders of magnitude. Micro-drilling of specific textures to unravel the simultaneous evolution of the sulfate and sulfide phases in Late Archean rocks will be used to better understand how it is that the early earth transitioned from an anoxic atmosphere to one with substantial amounts of molecular oxygen. PIs will collect new outcrop and drill core samples during a field campaign to the Campbellrand Platform in South Africa and make hundreds of new sulfur isotope measurements on these samples. Their goal is to create a history of seawater sulfate evolution during this key moment in earth history.